The major function of a telecommunications (“telco”) network device such as a switch, router or hybrid switch/router is to transfer network data or packets between various physical interfaces or ports on the network device. The ports are connected to external network attachments, for example, optical fibers, coaxial cables and twisted pair cables. Typically, a network device includes multiple forwarding cards (i.e., printed circuit boards or modules) coupled with the external network attachments through the physical interfaces. Network packets are transferred between forwarding cards through a switch fabric.
In older network devices, the switch fabric functionality was spread out or distributed amongst the forwarding cards—that is, the network device included a totally distributed switch fabric. As the size and complexity of network devices has increased, the number of signals/etches required to connect distributed switch fabrics has significantly grown. To avoid having to route these signals through the network device's mid-plane or back-plane, network devices began locating the switch fabric functionality on one card or printed circuit board (“central switch fabric”). As the size of network devices has continued to grow, the switch fabric functionality has also continued to grow such that to accommodate larger numbers of signals, central switch fabrics are often segmented into one or more cards and/or separated into a separate network device that is connected to the original network device through external network attachments, such as optical fibers. These external network attachments can be very expensive and a separate switch fabric port card may be necessary in the separate switch fabric device for each forwarding card in the original network device.
Since network devices are very expensive, the average network manager typically only purchases a minimally configured network device—that is, a network device with only the minimal functionality needed to service existing customers. The network manager then adds functionality to the network device as additional service requests are received. This allows the network manager to spread out the cost of a network device in proportion to the fees being received from customers.
For current network devices with central switch fabrics, a minimal configuration includes everything but the forwarding cards and physical interfaces. As requests for service are made, the network manager adds forwarding cards and physical interfaces as necessary. Consequently, for current network devices, even a minimal network device configuration requires a full switch fabric subsystem (one or more cards or a separate box) such that even a minimal network device configuration is very expensive. In addition, most network devices include a redundant switch fabric subsystem to take over should the primary switch fabric subsystem fail. Thus, the cost of a minimally configured network device is increased substantially by the cost of a second switch fabric subsystem.